Balanced wave guide branching system



y 1954 c. F. EDWARDS 2,679,582

BALANCED WAVE GUIDE BRANCHING SYSTEM Filed Dec. 24, 1945 FROM BEAT/N6 OSCILLATOR INPUT (3. I3 70 3.5.! m WAVELENGTH!) FIG. 2 FIG. 3

a "5*. *3 i: 22 k z 7' o l l 0,3 I Cg/ an 3.2 a: :14 as as C Ft' mvamarn 11v CENT/METERS C L m l INVENTOR i2: C F EDWARDS w A B) A TTORNEY Patented May 25, 1954 BALANCED WAVE GUIDE BRAN CHIN G SYSTEM Charles F. Edwards, Red Bank, N. .L, assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application December 24, 1945, Serial No. 637,124

11 Claims. 1

This invention relates to a wave transmission system employing a branching arrangement of dielectric wave guide lines and particularly to impedance matching devices for use with such a branching arrangement.

The invention is specifically applicable to a branching arrangement of a type first disclosed in the copending patent application of W. A. Tyrrell, Serial No. 470,810, filed December 31, 1942, now United States Patent 2,445,896, granted July 27, 1948, in which two branch sections of straight hollow pipe wave guide of elongated rectangular cross-section, disposed at right angles to each other, are joined to a main section of similar wave guide at an intermediate, common junction point in the electric plane, equivalent to a series electrical connection, and in the magnetic plane, equivalent to a shunt or parallel electrical connection, respectively. Due to the dissimilarity (one series and one parallel) of the electrical connections of the two wave guide branches with the main wave guide in such an arrangement, these two branches are conjugate or in balanced electrical relation with respect to each other and the two collinear portions of the main wave guide on opposite sides of the common junction point are also conjugate with respect to each other, and are in unbalanced electrical relation with respect to each of the two wave guide branches. If then, a generator is connected to any one of the four branching wave guide portions formed by the two collinear portions of the main wave guide and the two branches thereto at the common junction point so as to cause wave power to be transmitted over that branch towards the common junction point, and suitable loads are connected to the other three branching wave guide portions, this power will be divided equally between the loads connected to the two adjacent wave guide branch portions and substantially no wave power will be developed in the load connected to the fourth, oppositely situated, wave guide portion. These characteristics make the above-described branching wave guide arrangement particularly suitable for use in connection with a balanced modulator or converter to provide the desired distribution of wave energy between its input and output branches, especially with respect to the balanced electrical relation or condition of no wave power transfer which may be caused to exist between the oppositely situated wave guide branches, and to eliminate noise introduced by the associated local oscillator.

An object of the invention is to provide maximum transfer of wave energy over a wide band of frequencies between the input and output branches of such a wave guide branching arrangement.

A more specific object is to provide optimum impedance matching, and thus minimum reflection of wave energy, over a wide band of frequencies between each of two conjugately connected input wave guide branches and each of the two other (output) Wave guide branches in the above-described type of wave guide branching arrangement.

These objects are attained in accordance with the invention by the use of two properly dimensioned and located metal rods, one of which is tapered, at the junction of the two branch wave guides with the main wave guide in the above-described branching arrangement. The tapered metal rod, which extends across the interior of the main wave guide at the common junction point into the interior of the particular wave guide branch connected to the main wave guide in the electric plane (series electrical connection), to be referred to hereinafter as the E-plane branch, in the direction of the longitudinal axis of the latter branch, serves to match the wave power from the other wave guide branch, that joined to the main wave guide in the magnetic plane (shunt electrical connection), which will be referred to herein as the H-plane branch, over a. wide band of frequencies to the loads connected to the ends of the main wave guide. The second metal rod, which is connected across the interior of the E-plane wave guide branch between the wider faces of the latter at a suitable distance from the junction with the main wave guide and from the axis of that guide, serves to match the wave power from the E-plane wave guide branch over a wide band of frequencies into the loads at the ends of the main wave guide.

A better understanding of the invention will be obtained from the following detailed description when read in conjunction with the accompanying drawings in which:

Fig. 1 shows a perspective view, partially broken away, of a wave guide branching circuit embodying the impedance matching arrangement of the invention, applied to a balanced modulator or converter for use in a signal receiver of the superheterodyne or double detection type operated over a wide band of high frequencies;

Figs. 2 to 4 show sectional views along the lines 22, 3-3 and l4, respectively, of Fig. 1, drawn full scale, illustrating the detailed construction of the impedance matching arrangement of the invention;

Fig. 5 shows schematically the output electrical connections of the balanced crystal detectors employed in the balanced modulator of Fig. i; and

Fig. 6 shows curves plotted from experimental data illustrating the improvement attained by the use of impedance matching devices of the invention in connection with the wave guide branching arrangement of Fig. l. a

In the balanced modulator of Fig. 1, two straight sections I and 2 of x 1" rectangular wave guide of any length are joined as branches to a main straight section 3 of 1/ x1" rectangular wave guide, the three wave guides lto '3 being relatively disposed so that their longitudinal axes extend in mutually perpendicular directions from a common junction point. The wider (1) faces of the branch wave guide I are normal to the directicn' in 'whic'hthe inain wave guide 3 extends, and the narrower "faces of branch-guide l are parallel to'that direction. This-is-a-connection in the electric plane, that is, the plane parallel'to the lines of electric intensity produced in both joined 'waveguide's'when dominant waves are "pi'cpagatedover on'eofthem towards the junction between the two guides, "and is equivalent to a series electrical cOnnectiOn-ofthe two guides. The narrower' /2) "faces ofthe branch wave guide2are' normal to the direction in-which the main guide 3 extends and the wider (1 "faces of branch" guide 2 are'parallel to that direction. This is accnn'e'ctio'n inthe so-called magnetic plane, thatis,"the lines of electric intensity produced in both joined guides when dominant waves "are propagated over one'of the'm towards the junction between the two guides,which is"equiva lent--to-a-shunt or parallel electrical connection. The branch guide i connected to the r'nain' wave' guide'3 in the electric plane will be referred "to as the 'E--plane branch and 'thebranch wave guide 2 connected to the mam waveguide "3 in'the magnetic-plane as'the H-plane branch. i

The two branch portions Oia'nd' Ozof the main wave guide '3 respectively extending on opposite sides' of the'common junction with the branch waveguides l 'and'2 are of equallengthand-are closed at theirouterends by 'reflecting-plates, as

indicated. Equ'ivalent crystal-detectors n1 and D2 utiliZed inthe balanced modulator -or detector are connected in series with the'condensers C1 and C2, "respectively; between the widerfaces of" the re'spectivebranch portions 01 and Oz'of w the main waveguide'iiat'pointsequidistant from the common junction with thebr'anchwaveguides land 2,'near the"closed'endsof the main wave ui The high frequency inc'cmir'ig'signal power is applied to the balancedinod'ulator through the H-plane wave guide branch '2 and the local beating oscillator-power is applied to the'modulator through the e-piane waveguide branch I. Because of the conjugate "relation of these two branches and the equal resistance terminations of the two branch parades Ofand 02 of the main guide. thesignal'wave power from the H-plane branch will be divided at the junction 'withthe main guide3 between the portion O'r'and 02 of that guide, and none of this power-will enter the E-plane-branch. Similarlyg-the beating oscillator power from the 'Eplane'-branch-'will be divided at the junctionwith the -'main wave guide s-between the two main guide branches-O1- andorand ncne plane perpendicular to the detectors is such that the input of metal rod 4 having of this power will be fed into the H-plane branch. The loss of signal power into the beating oscillator branch and the transmission of beating oscillator power to the signal branch are thereby effectively eliminated. The portions of the signal and beating oscillator power entering the branches or and 02 of the main wave guide 3 will be combined in the crystal detectors D1 and D2, respectively to produce waves of intermediate frequency. The phase relationship of the intermediate frequency waves so produced in the two two detector outputs must be connected in series in order that the two waves-may combine in phase. The phase relationship of intermediate frequency waves produce'd'by two sources of power in the same branch are such that they may be balanced against one another by such a series connection to give no output, "and, therefore, noise components introduced by the beating oscillator can be effectively balanced out in balanced windings of athreewinding transformer T coupling the outputs for the two crystal detectors D1 and D2 through condensers C1 and C2, respectively in parallel'to the the intermediatefrequency amplifier of the superheterodyne signal receiver (Fig. 5)

To obtain 1 maximum transfer of wave energy overa wide band of high frequenciesibetweenithe input and output branches of :such a ibalanced modulator, impedance matching devices inlaccordance with the invention are utilized at the common junction of these branches.

As shown in Figs. 1 to 4,one .of thesel-impedance matching devices comprises a-tapered itslarger end affixed to the lower one of the'wider faces of the main wave guide 3 at a point equidistant from thetwo narrower faces of the H-plane wave guide branch 2 and nearer one of the narrower faces of the E- plane branch l than theother, and its tapered end extending to a given point intotheinterior oi the E-plane wave guidebranch l inthe direction of the =longitudinal axis of the latter. in the case of the particularljunction shown-utilizing /2 x 1" wave guide, the optimumdimensionsand location of the rod las experi'mentallyfdetermined are as follows:

Distance of center line-of rod-4 from one narrower face of main wavezguide' 3---..-10'354 The tapered rod" 4 serves'to" match 'over 'awide range of high frequencies'the signal power from the H-plane wave guide branch 2 into'the two crystal loads Di'and D2 connected to the branches Grand 02, respectively, of the main waveguide'3 at points equidistant from the'common' junction point. When no impedance matching devices were pres'ent,the measured value'of the standing wave ratio (SWR) looking into the H'-pl'ane branch 2 was foundtobe' 9.8 'decibles and that looking into the E-'plane'branch'6:0 'decibelsfor input energy of 3.33 centimeters wavelength with the load branches O1 and O2 terminated as shown. By means of the tapered'rod'A withthe optimum dimensions and location specified'above, the measured value of thestanding' wave ratio in the H-plane branch wasreduced' to 10.2 decibel for input energy of 3.33 centimeterswavelength and was made less than: l i decibel ati all-wavelengths between i 3.13 and 3153 centimeters,'sas shown by the lower curveof Fig. 6. Therrod rl has only a small: effect'onthe standing wave ratio in the E-plane branch, and the purpose of the taper shown is to minimize this effect.

The cylindrical metal rod 5 was provided to match over a wide band of frequencies the beating oscillator wave power from Ill-plane wave guide branch I into the crystal loads D1 and D2 connected to the branches O1 and O2 respectively, of the main wave guide 3 at points equidistant from the common junction point. The rod 5 extends from one of the widerfaces of the E-plane wave guide branch I to the other in a direction perpendicular to the longitudinal axis of that branch (and therefore parallel to the longitudinal axis of the main guide 3) at the proper distance from its junction with the latter guide and at the proper distance from the wall of wave guide I. After rod 4 had been filed to the correct dimensions given above, the standing wave was measured at various points alon the E-plane branch. From these measurements it was possible to determine the point where the resistive component of the impedance was equal to the characteristic impedance. It was observed that the reactive component of the impedance at this point was capacitive. The rod 5 was located at this point and in effect served as an inductive iris to cancel this capacitive reactance. In matching the E-plane and H-plane branches to the output wave guide, it is very helpful from an experimental standpoint to have the two procedures independent since the problem is greatly complicated by interaction effects.

For the junction utilizing /2". x 1" wave guide illustrated, the optimum dimensions and location for the rod 5 as determined experimentally are:

Inches Diameter of rod 5 A; Distance of rod 5 from junction of E-plane branch with main wave guide 3 0.200 Distance of rod 5 from one narrower face of E-plane branch 0.149

By means of the rod 5 having the optimum dimensions and location specified above, the standing wave ratio in the E-plane wave guide branch was reduced to 0.4 decibel at 3.33 centimeters wavelength and its variation with wavelength is shown by the upper curve of Fig. 6.

In converter and modulator applications of the above-described type of wave guide junction employing the impedance matching devices of the invention, it is preferable to employ the H-plane branch as the branch to which signals are applied since it provides somewhat better impedance matching over a wide band of high frequencies. The 3-decibel standing wave ratio obtained in the E-plane branch is negligible when this branch is used for introducing the beating oscillations.

It is understood, of course, that the device may be used at other wavelengths by the use of difierent size wave guide or at the same wavelengths using different size wave guide than those disclosed in the specific embodiment and that the dimensions and locations of the impedance matching elements may be varied to match other wave guide sizes and to operate at other wavelengths.

Various other modifications of the arrangements illustrated and described, which are within the spirit and scope of the invention, will occur to persons skilled in the art.

What is claimed is:

1. In combination with a wave transmission network consisting of three branching hollow pipe wave guides each of elongated rectangular cross-section, extending longitudinally in mutually perpendicular directions from a common junction point with the wider faces of two of said I guides normal to one of said directions and the wider faces of the third guide normal to another of said directions, one of said two guides extending longitudinally to each side of said common junction point, means to cause electromagnetic wave energy to be propagated over the other of said two guides towards said junction point, and a load connected near each end of said one guide, impedance matching means including a metal rod at the common junction of said three guides extending across the interior of said one guide to a given point in the interior of said third guide in the direction of the-longitudinal axis of the latter guide.

2. The combination of claim 1 in which the dimensions of said metal rod and its locationwith respect to said three guides are selected so as to obtain an optimum impedance match between said other guide and the portions of said one guide on each side of said junction point over a wide frequency range.

3. The combination of claim 1 in which the dimensions and relative location of said metal rod with respect to said three guides are selected so as to match the wave power from said other wave guide into the load connected near each end of said one wave guide over a wide frequency range.

4. The combination of claim 1 in which the largest lateral dimension of said metal rod is small compared to the dimension of the shortest side of the cross-section of any one of said three guides, and its length is substantially one and one-half times the dimension of the shortest side of the cross-section of said one wave guide.

5. The combination of claim 1 in which said metal rod is located nearer to one of the two narrower faces of said one wave guide than to the other and substantially equidistant from the two narrower faces of said other guide and from the two wider faces of said third wave guide.

6. The combination of claim 1 in which said metal is tapered in the direction towards the interior of said third guide to minimize the effect of this rod on the standing wave ratio in said third guide.

'7. In combination, a main hollow pipe v rave guide and two other wave guides branching out therefrom at a common intermediate junction point, the three wave guides having elongated rectangular cross-sections with the same corresponding dimensions, and extending longitudinally in mutually perpendicular directions with the wider faces of the main wave guide and one of said branch guides normal to one of said directions and the wider faces of the other of said branch guides normal to another of said directions so that said one branch guide and said other branch guide are connected in parallel and in series electrical relation, respectively, with said main guide, means for causing electromagnetic wave energy to be propagated over each of said branch guides toward said common junction point, a load connected to theportion of said main wave guide on each side of said common junction, and means for causing a maximum transfer of wave energy over a wide range of frequencies between each of said branch wave guides and the portions of said main wave guide on each side of said common junction point, comprising a tapered metal rod extending across the interior of said main wave guide at said common junction point into aorrswsa:

theinterior of :saidother :branch guide in the die-.- rection of the longitudinal :axis of the: latterguide; and a second cylindricalmetal rodextende ing acrosstheinteriorofsaid-"other guide :be tweenthe wider faces thereofaat a given distance fromits junction with said main wave'guide: w

8..'I'he combinationtof claim: 7 in: which-theadistance of said second metal rod'fromthedunctionof said other branch" guide-'with-saidz-main guide is approximately, equal to one-fifth the length of the longest side-of the rectangularv cross-esectionof. each of 'said guidesand its 1dis-' tance from one'of'thesnarrower faces of said other branch guide is'approximately equal toone-sev enthof the length of thelongest sideof the crosssection? of. said other guide 9. The combination. of 'claim- 7 in which said.

wave energy propagated over each of said branch."

wave guides toward said. common junction. point comprises signal oscillations and beating oscillations; respectively, the loads connected to the portions of said mainiwave-guide onxeach side of said common junction point comprise matched tosaid main wave-guide section and to-each otli er, extending outwardly from said main waveguide section;

11'; A wave-guide"assemblycomprising: a main wave-guide section :having:.a crystal detector at.

each. of the oppositenends' thereof oneside'rofeachofzsaid crystal detectors being capacitively: coupled to said 'main wave-guide section; and'am pair'of branch wave-guide sections, perpendicuw lartosaid .main wave-guide section and to' each":

other extending. outwardly from said main wa've guide section.

No references cited. 

